Analysis of the effects of nonidealities of power components and mains voltage unbalance on the operating behavior of a three-phase/switch buck-type unity power factor PWM rectifier

According to the experimental analysis of a 5 kW wide input voltage range three-phase three-switch buck-derived unity power factor PWM rectifier, the ideally constant DC output current does show a low-frequency distortion for open-loop control operation which is translated into low-frequency harmonics of the mains current. This distortion cannot be eliminated completely by closed-loop control since the controller bandwidth has to be limited for stability reasons and/or in order to avoid an excitation of the LC input filter. In this paper the parasitic effects being responsible for the low-frequency distortions of DC output voltage and/or current are analyzed analytically and quantified for different operating conditions. Furthermore, the minimization of the influence of the parasitic effects by proper pre-control is discussed. All theoretical considerations are confirmed by digital simulations